This invention relates to an optical network system for use in carrying out optical communication among a plurality of communication stations.
A conventional optical network system of the type described comprises a star coupler for optically coupling communication stations in common through optical fibers. The star coupler serves to distribute, to all of the communication stations, each optical signal train given from the communication stations and is, therefore, operable as a common transmission path. This means that such a system forms a logical bus architecture, as called in the art.
The optical network system is advantageous as compared with a coaxial cable network system because the optical network system is not subjected to any electrical troubles, such as electro-magnetic induction, and enables high speed and long-distance transmission.
Each communication station is usually connected to a terminal unit or units, such as a facsimile system, a personal computer, and any other intelligent terminal. Inasmuch as each terminal unit carries out communication at random independent of the other terminal units, such communication is often concurrently carried out in at least two terminal units. Concurrent communication inevitably gives rise to collision in the network system of the above-mentioned architecture. Such collision should rapidly be detected and removed. However, a long time has been necessary to detect the collision when a distance becomes long between the communication stations because a transmission delay of the optical signal train increases as the distance is lengthened.
Inasmuch as the star coupler has input and output terminals each of which is equal to a predetermined number and can only accommodate the communication stations to the predetermined number at most, the conventional optical network system is restricted in the number of the communication stations to be connected to the star coupler.